Sea Floor Spreading

---

Vocabulary

---

Mid Ocean Ridge - THe undersea mountain chain where new ocean floor is produced.
Sonar - A system that determins the distance underwater by recording the echos.
Sea-floor Spreading - THe process by which molten material adds new oceanic crust.
Subduction - Process by which ocean floor sinks.

Outline

---

• Mapping the Mid-Ocean Ridge

  • The East Pacific Rise is a part if the mid-ocean ridge
  • The mid-ocean ridge is the longest chain of mountains in the world.
    • A little bit of the mid-ocean ridge is on top of the water.
    • The island of Iceland is a part if the mid-ocean ridge that pokes on top of the water
  • Scientists use sonar to map the mid-ocean ridge
    • Sonar is a divice that bounces sound waves of underwater and records the echos of these sound waves.

• Evidence for sea floor spreading

  • Harry Hess was one of the scientists who studied the mid-ocean ridge.
    • He began to think about continental drift
      • He thought Wegener was right.
      • He thought the ocean floor moves like conveyor belts, taking the continents with them as they move.
        • This movement begins at the mid-ocean ridge.
          • The mid-ocean ridge forms along a crack in the oceanic crust.
          • Molten material rises from the mant;e and erupts
          • The molten material then spreads out, pushing the older rocks to the side.
          • As the molten material cools, it forms a strip of rock.
            • Harry Hess called this "sea-floor spreading"

• Evidence from molten material

  • In the 1960's scientists found evidence that new material is erupting along the mid-ocean ridge.
    • Scientists dived down to the bottom in a small submersible named "Alvin"
      • They saw strange rocks shaped like pillows or like toothpaste squeezed from a tube.
        • These rocks only can form when molten material hardens quickly after erupting underwater.

• Evidence from magnetic stripes

  • Scientists studied patterns in the rocks of the ocean floor, they found more evidence in sea-floor spreading.
    • Evidence shows that Earth's magnetic poles have reversed themselves 780,000 years ago.
      • The rocks that makes up the ocean floor lies in a pattern of magnetized "stripes"
        • These stripes hold a record if reversals in Earth's magnetic field.
          • Rock that hardens at the same time has the same "magnetic memory"

• Evidence from drilling samples

  • A ship called The Glomar Challenge, sent drilling pipes underwater to drill samples of the oceanic crust.
    • The farther away the rocks were, the older the rocks were.

• Subduction at deep-ocean trenches

  • A deep-ocean trench is a deep underwatercanyon.
    • Where there are deep-ocean trenches, subduction takes place.
      • Subduction is the process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle.

• Subduction and Earth's oceans

  • Because of the process of subduction and sea-floor spreading, ocean floor is renewed about every 200 million years.
    • That's the time it takes to form at the mid-ocean ridge, move across the ocean, and sink into a trench.

• Subduction in the Pacific Ocean

  • The vast of the Pacific Ocean covers one third of the planet.
    • The pacific ocean is shrinking.
      • Sometimes a deep-ocean trench swallows more oceanic crust than the mid-ocean ridge can produce.
        • If the ridge doesn't add new crust fast enough, the width of the ocean will shrink.

• Subduction in the Atlantic ocean

  • The Atlantic Ocean is expanding.
    • The Atlantic Ocean only has a few short trenches.
      • The spreading ocean floor has nowhere to go.
        • Over time, the Atlantic Ocean gets wider.

Back to Homepage